| In this dissertation, we present a precision measurement of the 1 s2s 1S0 -- 1 s2p 3P1 intercombination interval in the moderate-Z helium-like ion, 28Si 12+, using a fast-beam laser resonance technique. This experiment is a second-generation measurement designed to surpass the precision of the previous measurement of Redshaw et al. (Phys. Rev. Lett., 88 (2002) 023002), using an improved laser setup designed to cancel the Doppler shift. This was accomplished by incorporating a counter-propagating laser at 1,450 nm into the previous setup that used a co-propagating laser at 1,319 nm to induce the same transition. Our final result for this energy interval is 7,230.585(6) cm-1 with an overall precision of 0.8 parts-per-million (ppm). This result represents a 30-fold improvement over the previous measurement, and tests QED contributions at the level of 13 ppm. The two-electron atom/ion is a fundamental atomic system, and continues to be the subject of major theoretical work today. Hence, our precise measurement provides a clear test of modern theory, including higher-ordered QED effects. |
